This never happens. Him walking. And if he walks, he never holds your hand. He doesn't run. He's usually hanging on your leg sobbing that you aren't holding him. And he never holds your hand. During this walk, Mark even noted this rare moment. I think you can actually see Mark's smile lines busting a few new creases.
And within seconds, the moment was gone.
But there is a bright side: he was walking on his own without a single tear.